Add built-in Qoder ACP support

[xinyuan0801]

Summary

• add built-in qoder -> qodercli --acp support and sync the neutral built-in docs surfaces
• add the small Qoder compatibility needed in AcpClient for clean ACP stdio runs and Qoder CLI startup flag forwarding
• persist session options so forwarded Qoder startup flags survive named-session reuse, queue-owner restarts, and session/load recovery
• add regression coverage for registry mapping, client behavior, session persistence, and integration flows

Why

Qoder CLI already supports ACP over stdio, but acpx did not have a built-in entrypoint for it.

Real local ACP smoke also exposed two gaps: Qoder emits benign non-JSON shutdown chatter after successful runs, and Qoder-native startup flags derived from acpx session options would disappear after persistent session reuse unless they were stored in the session record.

This change makes acpx qoder ... work out of the box without adding new generic CLI conventions.

Validation

• pnpm run check
• pnpm run check:docs
• real local qodercli smoke for exec, JSON output, --file, named-session reuse, history, status, set-mode, cancel, --no-wait, approve-reads, and session/load recovery

AI-assisted and fully tested locally.

[xinyuan0801]

@steipete @vincentkoc could you take a look when you have a chance?

This adds built-in Qoder ACP support plus the small runtime/session persistence compatibility needed for real qodercli flows.